1. Field of the Invention
The present invention relates to a network system that includes a plurality of nodes that include a wireless communication function and that carries out data communication via the nodes.
2. Description of the Related Art
Recently, when carrying out data communication, an ad-hoc network such as a wireless local area network (LAN) is used. The wireless LAN includes only nodes that do not necessitate access points and can be connected wirelessly. In a connection topology of the ad-hoc network, a communication frame transmitted from a source node of data is relayed by another node and transferred to serially connected adjacent nodes. Thus, a communication path is formed from the source node to a destination node.
In the ad-hoc network, because a plurality of communication paths exist from the source node to the destination node, a method is necessitated to select the optimum communication path from the multiple communication paths.
In a commonly used communication path selecting method, an adjacent node having strong radio wave strength is selected as a transfer destination of the communication frame. In another commonly used communication path selecting method, a communication path of a smaller hop number from the source node to the destination node is preferentially selected as the communication path.
However, the optimum communication path cannot be always selected by using the method that preferentially selects the adjacent node having strong radio wave strength or by using the method that preferentially selects the communication path of smaller hop number. To overcome the drawback, for example, in a method disclosed in Japanese Patent Application Laid-open No. 2005-323266, the source node controls communication evaluation values of all the nodes that are included in the ad-hoc network and determines the optimum communication path.
However, in the conventional technology mentioned earlier, because the source node needs to control the communication evaluation values of all the nodes included in the ad-hoc network, a load on the source node significantly increases.
In other words, an increase in the load on the source node necessitates resources for the source node that are higher than resources such as a processing capacity and a memory size that are required for an original communication process of the source node. Due to this, a cost of the source node substantially increases compared to a cost of normal nodes. Moreover, if the source node is battery-driven, a process that calculates the communication evaluation values of all the nodes included in the ad-hoc network, causes a sharp increase in power consumption and a reduction in operating time. Thus, the drawback mentioned earlier is further aggravated.
In other words, in the ad-hoc network, selecting the optimum communication path without putting a load on the source node and carrying out data communication is of significant importance.